Abstract

Rapid progress has been made on brassinosteroid (BR) signaling in Arabidopsis. However, little is known about BR signaling in monocotyledon. Here, we characterized a rice dwarf and low-tillering (dlt) mutant and cloned the corresponding gene via map-based cloning. DLT encodes a new member of plant specific GRAS family. The dwarf phenotype of dlt is mostly similar to BR-deficient or signaling mutants in rice. In addition, both lamina inclination and coleoptile elongation assays show that dlt is insensitive or much-less responsive to brassinolide (BL), the most active BRs, suggesting that DLT is involved in BR signaling. Consistent with the conclusion, the accumulation of BR-biosynthesis genes in dlt mutant indicated DLT is involved in feedback inhibition of BR biosynthesis genes. In addition, several other BR-regulated genes are altered in dlt mutant. Finally, consistent with the fact that DLT is also negatively feedback-regulated by BR treatment, gel mobility shift assay showed that OsBZR1 can bind to DLT promoter through the BRRE element. Taken together, we identified a new signaling component that is involved in several specific BR responses in rice.